A starter or choke unit of this kind is known from Swiss Pat. No. 465,058. In this unit, a snap toggle switch is used which is actuated mechanically by means of a tilting spring. The snap toggle switch is actuated after the power-supply switch has been opened. The polarity reversal exciter coil of the snap toggle switch is exposed to the direct current of the lamp. However, the contact device is not moved thereby; instead, a movement of the relay armature only tenses the spring. Only when the electrical circuit of the lamp is broken by a shutoff of the power supply does the lamp current gradually drop to zero, after the discharge of the capacitances of the rectifier-multiplier circuit; and only then does the polarity reversal spring throw over the contact device of the snap toggle switch, in a practically load-free manner. Nevertheless, the switchover is not entirely load-free, and scorching of the contacts thus occurs. Furthermore, each line of lamps requires a suitably adapted polarity reverser exciter coil.
In another known apparatus for supplying power to gas discharge lamps (East German Pat. No. 92,763), all the switching elements are disposed in a metal housing embodied by a starter or choke coil, wherein a short-circuit element is provided. When the apparatus is switched on, the short-circuit element is drawn up, so that the armature movement can be utilized in order to actuate a switchover device when the gas discharge lamp is switched on or off, thus preventing the occurrence of cataphoresis.
Finally, in a further known apparatus for powering gas discharge lamps (West German laid-open application 2 116 812), a pushbutton reversal switch which is actuated with the aid of an electromagnet is provided as the switchover device.
The operation of gas discharge lamps on an alternating-current power supply via rectifier-multiplier circuits has major advantages as compared with direct-current operation; specifically, there is an energy saving of up to 30% resulting from the avoidance of recombination losses in the gas discharge path at each half-wave of the 50 Hz alternating-current power, and reduced losses in structural components of the rectifier-multiplier circuit as compared with copper and iron losses in known starter units. The rectified power supply enables flicker-free burning of fluorescent lamps, without a stroboscopic effect. A rectifier-multiplier circuit of this kind is known from West German Pat. No. 1,639,108 and enables direct starting. In long discharge lamps, that is, those having a length of over ca. 60 cm, however, a mercury vapor shift (cataphoresis) occurred, which can cause impoverishment of the mercury component in the anode region, which reduces the light yield. It has already been proposed to prevent this cataphoresis by means of mercury vapor equalization.